Voltage versus current sensing system

ABSTRACT

A voltage versus current function sensing system for use in conjunction with power supplies for electrochemical processes, and particularly for sensing arcing and sparking in the load circuit or for determining the value of resistance of the load, the load being substantially a resistive load. The system includes a shunt for sensing the load current in the output buss and a load voltage sensing circuit, the current being fed to a preamplifier and a four quadrature multiplier, the output of the multiplier being fed to the input circuit of a subtracter circuit, and the voltage signal also being fed to the input of the subtracter. The output of the subtracter is amplified and rectified and fed to a trigger circuit to control load current being fed to the output terminals of the power supply. The system also includes an automatic gain control feedback loop for the four quadrature multiplier, the feedback loop including a rectifier and inverter circuit for the voltage input to the subtracter and a rectifier circuit connected for the current input to the subtracter, the output of the voltage inverter and the output of the current rectifier being fed to a summing point. The summing point provides the input signal for a high gain driver circuit and the driver circuit provides the gain control signal for the four quadrature multiplier to cause the multiplier to provide an output current signal which is of equal magnitude to the voltage signal. The system also includes an automatic inductance or capacitance correction circuit which is responsive to the change in current with respect to time of the sensed current signal at the buss to correct for any inductance or capacitance which may be present in the output circuit of the power supply due to the natural impedance of the leads connected to the load.

United States Patent [72] Inventor Rudolf E. Six

Rolevllle, Midi.

[2l Appl. No. 880,701

[22] Filed Nov. 28, 1969 [45] Patented Aug. 31, 1971 [73] AssigneeUdylite Corporation Warren, Mich.

[54] VOLTAGE VERSUS CURRENT SENSING SYSTEM 16-22, 20,-22 T, 22 SC;307/52-54; 204/323, 327

[$6] Reierenees Cited UNITED STATES PATENTS 3,487,291 12/1969Dowgiallo,Jr 323/20 3,517,301 6/1970 Huber 323/20 PrimaryExaminer-Gerald Goldberg Attorneys-Peter F. Casella, Donald C. Studley,Richard P.

Mueller and James F. Mudd ABSTRACT: A voltage versus current functionsensing system for use in conjunction with power supplies forelectrochemical processes, and particularly for sensing arcing andsparking in the load circuit or for determining the value of resistanceof the load, the load being substantially a resistive load. The systemincludes a shunt for sensing the load current in the output bus and aload voltage sensing circuit, the current being 7 fed to a preamplifierand a four quadrature multiplier, the output of the multiplier being fedto the input circuit of a subtracter circuit, and the voltage signalalso being fed to the input of the subtracter. The output of thesubtracter is amplified and rectified and fed to a trigger circuit tocontrol load currentbeing fed to the output terminals of the powersupply.

The system also includes an automatic gain control feedback loop for thefour quadrature multiplier, the feedback loop including a rectifier andinverter circuit for the voltage input to the subtracter and a rectifiercircuit connected for the current input to the subtracter, the output ofthe voltage inverter and the output of the current rectifier being fedto a summing point. The summing point provides the input signal for ahigh gain driver circuit and the driver circuit provides the gaincontrol signal for the four quadrature multiplier to cause themultiplier to provide an output current signal which is of equalmagnitude to the voltage signal.

The system also includes an automatic inductance or capacitancecorrection circuit which is responsive to the change in current withrespect to time of the sensed current signal at the bus to correct forany inductance or capacitance which may be present in the output circuitof the power supply due to the natural impedance of the leads connectedto the load.

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SHEET 1 BF 3 VOLTAGE vensus CURRENT SENSING SYSTEM BACKGROUND ANDSUMMARY OF THE DEVELOPMENT This invention relates generally to anautomatic voltage versus current sensing circuit for use in connectionwith a power supply, and more particularly to an are or spark sensingcircuit, in the case of an electrochemical machining system, or aresistance measuring circuit in the case of an electrochemical paintingor other type of variable resistance load process. In the former case,an incipient arcing or sparking is sensed and utilized to immediatelylimit the current being fed to the load and ultimately to shut down thepower supply or, in the latter case, to provide a measure of theresistanceof the load for control purposes.

in certain electrolytic processes, particularly those utilizing a gapcomprising a tool electrode and a workpiece, there arises certainconditions which are highly deleterious to the workpiece on which theoperation is being performed and also on the apparatus being utilized.Referring'specifically to electrochemical machining processes, atoolelectrode is brought into proximity with the workpiece and anelectrolyte is directed between the workpiece and the tool electrode. Aselectrical energy is applied between the workpiece and tool electrode,material removal from the workpiece occurs. While the material removalprocess isnot totally understood, it has been found that certainconditions arise in the gap which causes the gap to arc or spark,thereby: causing pitting and deterioration of the tool electrode and,further, damage to the finish being applied to the workpiece.

One theory as to the cause of the above conditions in the gap relates tothe flow, of impurities suspended in the electrolyte being passedthrough the gap, whether theimpurity be of aninsulating or a conductivecharacter. In the case of an insulating impurity, a portion of the areaof the tool electrode being presented to the workpiece is masked,thereby lessening the conductive area for the current flow. Accordingly,the current has a tendency to fall rapidly to presenta rapidlydecreasing current wave front. Simultaneously, the masking of theworkpiece due to the insulating character of the impurity causes a hillto form on the workpiece due to the lack of material removal from thearea masked by the impurity.

In certain instances, the impurity is washed away leaving the hill,which is of such a nature as to present a reduced gap to the toolelectrode. Thus, subsequent conduction tends to center about the hill,further sharply modifying the amount of current flow. On the other hand,in the situation where the impurity is of a conductive character, thegap is effectively short circuited due to the impurity, thereby causinga sharp rise in current. Similarly, the rise in current presents a steeprising.

current from to the source of electrical energy and a correlative dropin voltage across the workpiece. A similar situation occurs inelectrochemical polishing and other electrochemical processes of thistype. V

In order to protect both the tool electrode and the workpiece, it isnecessary that the incipient sparking ro arcing be sensed as soon aspossible after occurrence thereof and to control the operation of thepower supply to substantially reduce the current flowing to the load.The earlier the. sparking is sensed and adjusted, even to the point ofshutting down the power supply, the greater protection provided theworkpiece and tool electrode. The normal circuit protectors beingutilized in conjunction with such power supplies have not beensufficiently fast acting to preclude damage of this type.

Also, it has been found desirable to provide a control circuit which isresponsive to the above described conditions at the load and notresponsive to the other conditions in the electrical circuit, as forexample in the power supply. Thus, a system has been devised to maintainthe current flow through the gap at a maximum in order to achieve thegreatest material removal from the workpiece, However, in certaininstances,

this high gap current will cause the aforementioned arcing or sparking.The system of the present invention is capable of maintaining thismaximum current while affording instantaneous protection of theworkpiece and tool electrode in the event sparking or arcing occurs.

Further, it has been found that, in the electrochemical painting art,the density or thickness of the paint layer applied is a function of theresistance of the load. Accordingly, the system of the present inventionmay be utilized to derive a measure of the load resistance, and thus ameasure of the paint material being applied to the work, and utilizethis signal as a control for the power supply. This control could eithertake the form of a control for linearly increasing the successive layersof paint being applied or may be utilized to determine the finalthickness of paint being applied. In systems of this type, it is commonthat the paint is rapidly applied when the workpiece is first immersedand current applied due to the fact that the resistance of the load isextremely low, thus providing a high current flow. As the paint indeposited on the workpiece, this current flow is diminished in anonlinear fashion. Accordingly, the system of the present inventioncould be utilized to linearize the application of paint to the surfacethrough maintaining a linearly increasing resistance characteristic.

Accordingly, it is one object of the present invention to provide animproved control for a power supply.

It is another object of the present invention to provide an improvedcontrol for a power supply which utilizes a voltage versus currentcharacteristic.

It is a further object of the present invention to provide an improvedcontrol system'for controlling the operation of electrolytic processingapparatus.

It is still another object of the present invention to provide animproved control circuit for generating an output signal which is afunction of the load resistance.

It is still another object of the present invention to provide animproved arcing or sparking control system for controlling the output ofenergy from a power supply to an electrolytic load.

It is another object of the present invention to provide an improvedcontrol system for controlling the operation of a power supply or thecurrent being fed to the load in the case where the load is a highlyresistive load, system including means for compensating for anyinductive or capacitive impedance present in the output conductors.

It is still a further object of the present invention to provide animproved arc or sparksensing control apparatus which is capable ofrelatively correlating voltage and current magnitude.

It is still another object of the present invention to provide animproved power supply control system for controlling the energy beingfed to the load wherein the control system includes an automatic gaincontrol circuit for controlling the operating points of the varioussubsystems within the circuit.

It is still a further object of the present invention to provide animproved control system for generating a signal which is a function ofthe resistance of the load.

It is still another object of the present invention to provide animproved control circuit which is extremely fast acting in operation andreliable in use.

Further objects, features and advantages of this invention will becomeapparent from a consideration of the following description, the appendedclaims the accompanying drawings in which:

FIG. 1 is a schematic diagram in block form illustrating a preferredsystem incorporating certain features of the present invention;

FIG. 2 is a schematic diagram illustrating a portion of the system ofFIG. 1, and particularly the quadrature multiplier and the inductancecorrection loop;

FIG. 3 is a schematic diagram illustrating another portion of the systemof FIG. 1 and particularly the voltage and current rectifiers and theoutput trigger circuit; and

FIG. 4 is a schematic diagram illustrating a final portion of the systemof FIG. 1 and particularly illustrating the crowbar output rectifiercircuit.

With the system of the present invention, current and voltage signalsare derived from the output busses,'the voltage signal being exactly themagnitude of the voltage across the output buss and the current signalbearing a preselected ratio to the output current.

The current signal is fed through a series of amplifiers to boost thesignal to an equivalent magnitude to that of the voltage signal. Thesystem includes an automatic gain control circuit which senses both thecurrent and the voltage and compares these two signals to provide anoutput signal which is utilized as a multiplication factor in boostingthe current signal. Thus, the automatic gain control circuit insuresthat the current level is equivalent to the voltage level. The voltageand current signals are then compared and subtracted to provide anoutput signal for a trigger circuit which normally is at a zero level inthe case of normal conditions. However, if an abnormal condition, as forexample a spark or arc, occurs, the current signal will rise sharply andthe voltage signal will drop to produce an unstable condition in thesystem and provide an output triggering pulse. This triggering pulse isutilized to shunt the output current, shut down the power supply andsignal the operator.

As was stated above, it is important that the load be resistive inimpedance and, in order to compensate for any slight inductance orcapacitance in the load circuit including the buss leads, an automaticinductance correction or di/dt correction circuit has been provided.This correction circuit senses the input current and provides a signalwhich is fed forward and injected into the current amplification circuitafter the multiplication has taken place. Thus, the current signal isautomatically compensated for any inductance that may exist in the loadcircuit. Further, it has been found that the automatic gain controlcircuit provides a measure of the resistance of the load because theinput current is multiplied by the feedback factor to render the currentsignal exactly equal to the voltage signal. Thus this multiplicationfactor results in a measure of the resistance in accordance with Ohmslaw.

Referring now to FIG. 1, there is illustrated a block diagram of apreferred control system incorporating the features of the presentinvention which is adapted to be connected to the output bussing of apower supply, and particularly to a shunt which derives a current signalwhich is proportional to the load current flowing in the buss. The shuntis preferably of a noninductive type and a shunt manufactured by the T &M Research Company, Model No. K10,000- has been found particularlysuitable. The output of the shunt is fed to an input terminal 12, theterminal 12 being AC coupled with a preamplifier 14 be means of acapacitor 16. The preamplifier preferably has a gain of approximately50.

The output of the preamplifier 14 is fed to an input terminal of a fourquadrant multiplier circuit 20 by means of a conductor 22, the fourquadrant multiplier circuit 20 being of the type manufactured by theMotorola Corporation, Semiconductor Division, Model No. MCl595L or ModelNo. MCl495L. In the particular system to be described, the multiplier 20is interconnected to generate an output voltage which is a linearproduct of the two input voltages and provides extreme accuracy andlinearity in its operation. The four quadrant multiplier circuit 20 hasat least two inputs, an X and a Y input, the Y input being connected toan input terminal 24 from an automatic gain control circuit to bedescribed below. Accordingly, the four quadrant multiplier circuit 20will provide an output signal on an output conductor 28 which has amagnitude determined by the product of a constant times the inputvoltages on conductors 22 and 24. In the normal case, the constant is0.1 and this 0.1 XY signal is fed to an amplifier 30 by means of aresistor 32. The amplifier, in the preferred embodiment, is selected tohave a gain of 10 to compensate for the inherent reduction in theproduct signal created by the four quadrant multiplier circuit 20. Thus,the I out signal from the amplifier 30, as impressed on conductor 36,will be the product of the X and Y signals on conductors 22. 24respectively.

The output from the amplifier 30 is fed to a subtracter circuit 40 bymeans of an AC coupling element, in the fonn of a capacitor 42. Thevoltage, which is already at a level which may be compared to theamplified current level, is fed directly into the subtracter circuit 40by means of an input terminal 44 and a capacitor 46.

In order to insure that the current is maintained at a level which willprovide a substantially zero output at the output of system 10-duringnormal operation, a voltage signal is fed to an automatic gain feedbackcircuit 50 by means of a conductor 52 and a multiplied current signal isfed to the output gain circuit by means of a conductor 54. THe voltagesignal is fed through a rectifier circuit 56, which produces the outputwave form illustrated at 58, this signal being the full wave rectifiedvoltage signal having an amplitude a. Similarly, the current signal isfed through a rectifier circuit 60 to produce an output signal on anoutput conductor 62 having the wave form illustrated at 64, with anoutput level b. In the normal operation of the circuit, a and b willgenerally be of the same height due to the multiplication of the currentsignal described above. The outputs of both rectifiers 56 and 60 are fedto a summing node 66 by means of a pair of resistors 68, 70respectively. However, in order to derive a zero current signal at node66 in a situation where the amplitudes a and b are equal, the voltagesignal is inverted by means on an inverter circuit 74 and, with equalamplitudes of voltage and current signal will produce a zero current atnode 66.

The signal at node 66 is fed to a high gain driver circuit 78, whichdriver circuit provides a small driving current at an output conductorin response to a zero input current from node 66. However, if node 66should go slightly positive or negative, it being remembered that thecurrent signal may exceed the voltage signal or vice versa, the highgain driver circuit 78 will provide an extremely large output signal onconductor 80. This large output signal on conductor 80 is fed through asingle rolloff network 82, including a resistor 84 and a capacitor 86,to the conductor 24 which forms the Y or automatic gain input to thefour quadrant multiplier circuit 20. The network 82 is selected to besufficient to insure that the single rolloff point is achieved in thefeedback circuit, this avoiding oscillation or ringing and otherundesirable characteristics of a feedback circuit.

The automatic gain control signal impressed on conductor 24 is utilizedas the Y input to the four quadrant multiplier circuit 20, the Y inputbeing used as a factor to multiply the current signal impressed onconductor 22. Thus, the output signal on conductor 28 will be somemultiplied factor of the current signal on conductor 22, this multipliedfactor being determined by the difference between the voltage andmultiplied current signal. It will be seen that the signal on conductor22 is a current signal and the output signal on conductor 28 is equal tothe voltage signal being impressed on the voltage input conductor to thesubtracter circuit 40, after amplification by amplifier 30. Thus, thesignal on conductor 24 is the necessary signal to insure that thecurrent signal on conductor 28 is proportional to the voltage signal.

Therefore, according to Ohms law, the signal on conductor 22 ismultiplied by an automatic gain control signal on conductor 24 which isa function of the resistance of the load circuit. Thus, the signal onconductor 24 provides an indication of the resistance of the loadcircuit and may be utilized as a control signal in controlling theoperation of a power supply or other similar device providing power toan electrochemical painting system. For example, the signal on conductor24 may be compared to a reference level to shut off the paintingoperation after a preselected resistance is achieved, the signalindicating a preselected thickness of paint on the workpiece. Also, thesignal on conductor 24 may be utilized to control the application ofenergy to the painting load. For example, the resistance signal onconductor 24 may be utilized to nonlinearly increase the load current tothe painting load to maintain a linearly increasing resistance at theload.

As stated above, the subtracter circuit 40 subtracts the instantaneousvoltage and current signals being fed to the input circuit thereof toprovide an output signal at an output conductor 90 in the event asudden, opposite change in the voltage and current circuit occurs. Thischange could be due to a sudden arcing or sparking, as described above,whereby the current rises to a relatively large level in a short periodof timewhile the voltage drops. Normally, the input to the subtractercircuit 40 will be equal and a zero signal will be impressed onconductor 90. The signal level on conductor 90 is amplified by means ofan amplifier circuit 92 and fed to an output trigger circuit 94 by meansof a rectifier 96. In the event a sparking or arcing occurs, the triggercircuit is supplied with a trigger signal which will energize or providea firing pulse on an output conductor 98. The output conductor 98, aswill be seen hereinafter, supplies a firing signal for a controlledrectifier crowbar circuit and also provides a signal for turning off therectifier.

As stated above, it is substantially impractical to provide a purelyresistance load circuit due to the fact that a certain amount ofinductive or capacitive impedance will exist as created by the outputbusses and other circuit conductors. Accordingly, it has been founddesirable to correct for the presence of a slight amount of reactance inthe load. As can be seen from the foregoing description, it is importantthat the voltage and current signals be exactly in phase in order tosense the relative magnitudes of the voltage and current signals.Accordingly, a reactance correction circuit 100 has been provided toinject a compensating current into the output amplifier 30 in responseto a sensed rateof change of current with respect to time at the inputcircuit. The circuit 100 includes an operational amplifier circuit 102which receives an input from the current input by'means of a conductor104 and injects the output of the correction circuit 102 into theamplifier 30 by means of a resistor 106 and a conductor 108.

The circuit 102 basically comprises a differentiator circuit whichprovides an output signal proportioned to the rate of change of currentwith respect to time. It will be remembered that the voltage generatedbecause of the inductive reactance of a circuit is equal to theinductance times the change of current with respect to time. Theinductance in any circuit, once it is connected, is constant due to thefact that the inductance is a function of the mechanical characteristicsof the circuit, for example, the length and shape of the conductors.Thus, the generation of voltage which is proportional to the rate ofchange of current with respect to time will be a direct measurement ofthe inductance of the circuit. One example of the output of thedifferentiator correction circuit 102 is illustrated at 110 and is seento be the differentiation of the input signal illustrated at 112, whichinput signal is a half-wave wave rectified current after the control forthe output power has been fired late in the cycle. However, the waveforms in the remainder of the drawings illustrate the operation of thesystem assuming the full wave is being fed to the load.

In operation, the current input signal from the buss is fed through theinput terminal 12 from the shunt unit described above. This signal isfed through the preamplifier 14 to the four quadrant multiplier circuit20 wherein the signal on conductor 22 is multiplied by a constant andthe signal on conductor 24. The output of the four quadrant multiplieris fed to an amplifier 30, the output of which is fed to the subtractercircuit 40. Also, a voltage signal is provided input terminal 44 and isfed directly to the subtracter circuit 40.

The four quadrant multiplier circuit in conjunction with amplifier 30,the amplifier 30 providing the reciprocal of the constant on which thefour quadrant multiplier operates, is utilized to maintain the currentsignal at a level equal to the magnitude of the voltage circuit. Thus, avoltage signal is fed to a summing node 66 by means of a conductor 52, arectifier 56 and an inverter 74. The current signal, aftermultiplication, is fed to the node 66 by means of the rectifier 60. Thusif the two signals are identical and one is inverted'relative to theother, a zero output signal will be fed to the high gain driver circuit78. A zero input to the driver circuit 78 provides a slightdrivingcurrent to the four quadrant multiplier by means of conductor 24. Thus,the signal on the conductor 24 provides the multiplier circuit 20 withthe multiplying factor necessary to render the output signal onconductor 36 exactly equal to the voltage signal. Therefore, the signalon conductor 24 is a function of the resistance of the circuit.

Further, the nature inductance of the buss circuit is corrected by meansof the inductance correction circuit 102 which senses the buss currentand differentiates it to provide or inject a signal into the amplifier30 which is proportional to the rate of change of current with respectto time.

Further, the natural inductance of the buss circuit is corrected bymeans of the inductance correction circuit 102 which senses the busscurrent and differentiates it to provide or inject a signal into theamplifier 30 which is proportional to the rate of change of current withrespect to time.

The output of the subtracter, in the normal situation, is substantiallyzero to provide a zero signal to a trigger circuit 94. However, if thecurrent rapidly rises and the voltage drops, thus creating a multiplyingeffect, the system cannot correct with sufficient speed to preclude atrigger pulse being fed to the trigger circuit 94. When the triggercircuit 94 has been pulsed, the crowbar circuit will be actuated and therectifier shut off by means ofthe signal on conductor 98.

Referring now to FIG. 2, there are illustrated the details of theenvironment of the four quadrant multiplier circuit 20, the inductiveimpedance correction circuit 102 and the multiplied current outputamplifier circuit 30. It is to be understood in connection with FIGS.2-4 that identical reference numerals to those used in FIG. 1 will beutilized to represent like systems. Particularly, input current is fedfrom the input terminal 12, through a capacitor 128 and resistor 130, tothe inverting input of an operational amplifier 132 in preamplifiercircuit 14. The operational amplifier includes a capacitor 134 andresistor 136 combination for frequency stabilization of the input and acapacitor 138 for frequency stabilization of the output. Also, thenoninverting input is grounded through a resistor 140. Each of theelements, 134, 136, 138 and 140 are common to all of the operationalamplifiers to be described hereinafter and will not be further describedin connection with the following operational amplifiers.

The output of the preamplifier circuit 14 is fed by means of theconductor 22, to the four quadrant multiplier circuit 20 as describedabove. The output of the four quadrant multiplier circuit is fed to anoperational amplifier circuit 144 by means of a plurality of conductors,which conductors correspond to the conductors 28 described inconjunction with FIG. 1. The operational amplifier circuit 144 includesa plurality of input resistors 146, 148 and a feedback resistor 150 forcontrolling the operation of an operational amplifier 152. Theoperational amplifier 152 provides a summing of the two outputs on theoutput conductors 28 and also acts as a buffer stage for the signalbeing fed to the output amplifier circuit 30.

The output of the operational amplifier 152 is fed to the input circuitof the amplifier circuit 30, and particularly to the inverting input ofan operational amplifier 158 by means of a resistor 160. Again, theoperational amplifier 158 includes a feedback resistor 162 plus theother circuit interconnections described above.

FIG. 2 also illustrates the rate of change of current with respect totime correction circuit 102 which includes an operational amplifier 166,the input from input terminal 12 being fed to the inverting inputthereof by means of a conductor 168. The circuit of FIG. 2 illustratesthe input to the di/dt correction circuit being supplied directly fromthe input terminal by means of the conductor 168 and a capacitor 170.However, the capacitors 128 and 170 may be combined and connectedbetween the input terminal 12 and the conductor 168 as illustrated inFIG. 1. The output of the operational amplifier is fed by means of aconductor 174 and the resistor 106 in conductor 108 to the noninvertinginput of the operational amplifier 158. It will be noted that thecircuit of FIG. 1 indicates that the current correction circuit outputis fed to a summing node and thence to the inverting input of theamplifier circuit 30. This system can be utilized in the case whereproper polarity is taken into account to subtract the signal from thesignal being fed through resistor 32 or where the buss circuit iscapacitive. Otherwise, the correction circuit output should be fed tothe noninverting input of the amplifier circuit 30. This latterconnection is illustrated in FIG. 2 as a modification of FIG. 1.However, in the case of FIG. 2, if the load circuit is capacitive innature, the output of the operational amplifier 166 will be fed to asumming node connected to the inverting input of the operationalamplifier 158. Thus, it is purely a phase consideration if the inductiveload provides a signal on conductor 174 which is subtracted from thesignal being fed to the input circuit of the amplifier 30. In the caseof capacitive loads, the signal on conductor 174 is fed to be additivewith the input signal to the amplifier circuit 30.

The remaining connections to the four quadrant multiplier, includingamplifier 152, are those recommended by the manufacturer of the abovereferenced four quadrant multiplier circuit and particular reference ismade to the literature on that four quadrant multiplier for fullerunderstanding of the operation of the multiplier circuit 20. Further, aswill be seen from a further description of FIG. 4, the automatic gaincontrol input signal on conductor 80 will control the Y input to thefour quadrant multiplier circuit 20 and a provide the multiplier factorfor the current on conductor 22. It is the average of this signal onconductor 80 which is a measure of the resistance of the load at anytime. The single rolloff operation provided by capacitor 86 and resistor84 has been described above.

Referring now to the automatic gain control feedback loop, andparticularly to FIG. 3, it is seen that the voltage signal on thevoltage buss is fed through a capacitor 46 and then to the voltagerectifier circuit 56 by means of a conductor 180. The rectifier circuitincludes an operational amplifier 182 which is provided with an inputconductors 184, 186 connected to the inverting and noninverting inputsrespectively, the latter of which is grounded through a resistor 188.The operational amplifier 182 includes an input resistor 190 and a firstfeedback resistor 192. The feedback loop includes the resistor 192 and adiode 194 for one-half cycle and a resistor 196 and a diode 198 for theother half cycle fed to the input circuit. Thus, a sine wave input onconductor 180 will be fed to the input conductor 184 and the output at anode 200 will be an inverted half wave rectification of the input curve,with the negative input loops being zero at the output node 200. Thesenegative loops are generated through resistor 196 and diode 198 and arenot used.

The resistors 190, 192 are selected to be of the same value so that theoperational amplifier operates at unity gain. The signal on conductor180 is fed forward to a second node 202 by means of a resistor 204 andthe signal from node 200 is fed to node 202 by means of a resistor 206.Thus, the input signal on conductor 180 is fed forward to node 202,without inversion, for summing with the signal being impressed on node200. The resistor 206 is selected to be half of the value of theresistor 204. Thus, the signal from node 200 being fed to the node 202due to the positive half cycle of the input signal at conductor 180, isa negative half wave which is twice the amplitude of the positive halfwave being fed forward through the resistor 204. Thus, the summingnetwork results in a signal at node 202 which is the negative wave formof the positive half cycle introduced at conductor 180. During thenegative half wave of the input signal on conductor 180, the node 200 isat a zero potential and the negative half cycle is merely fed forward bymeans of resistor 204. However, the magnitude is reduced by one-half dueto the resistance 204. Thus, the signal at output conductor 202 is aninverted full wave rectification, at half magnitude, of the input signalon conductor 180. This signal at node 202 is fed to a second bufferoperational ampli-"t fier 210, and particularly to the inverting inputthereof at conductor 212, to provide a full wave rectification in thepositive direction of the input signal at conductor 180. This signal isillustrated at 216 and is impressed on an output conductor 218. Thus,the circuit 216 is an absolute value circuit.

The current rectifier circuit 60 is identical to that described above inconnection with the description of the voltage rectifier circuit 56.Particularly, the current circuit 60 includes an operational amplifier220 provided with the input resistor 222, the feedback resistor 224 andthe diode 226. The opposite half cycle is generated by means of aresistor 228 and a diode230. The circuit 60 further includes afeed-forward resistor 234 which is connected to a node 236, the outputof the operational amplifier 220 also being fed to the node 236 by meansof a resistor 240. The full wave rectified signal at node 236 is thenfed to an inverting buffer amplifier 242, which includes a feedbackresistor 244. The output of the current rectifier circuit is fed to anode 246.

Referring now to FIG. 4, the voltage signal at output terminal 218 isfed to the inverter circuit 74 by means of a resistor 248. The invertercircuit 74 further includes a feedback resistor 250 which is connectedbetween the input and output of an operational amplifier 252. The outputof the operational amplifier 252 is fed to the summing node 66 throughthe resistor 68 and the rectified current signal is fed directly fromthe input terminal 246 to the summing node 66 through the resistor 70.

The summing node 66 is connected to the high gain driver circuit 78, andparticularly to the inverting input of an operational amplifier 256. Theoperational amplifier includes a pair of back-to-back connected zenerdiodes 258, 260 to prevent the output from saturating into its limits torender the operational amplifier 256 an extremely fast and high gainamplifier. The output of the operational amplifier 256 is fed to theautomatic gain control conductor which is connected to the Y input ofthe four quadrant multiplier circuit 20 described in conjunction withFIG. 2. It is the average of this signal on conductor 80 whichrepresents a function of the resistance of the load circuit and alsoprovides a multiplication factor for the current signal.

Referring back to FIG. 3, the current and voltage signals beingimpressed on conductors 36 and 44 are fed through the capacitors 42 and46 to the subtracter circuit 40. Particularly, the current output signalis fed through a resistor 264 and then to the inverting input of anoperational amplifier 266 by means of a conductor 268. On the otherhand, the voltage signal is fed to the noninverting input of operationalamplifier 266 by means of a resistor 270 and a conductor 272. Theoperational amplifier 266 performs the subtracting operation between thesignals on conductors 268, 272 and provides a difference signal onoutput conductor 90. This difference signal will be minimal when thevoltage and current signals, after multiplication of the current signalare of equal magnitude and in phase. However, if the circuit is not fastacting enough to correct for changes in voltage and current,particularly in the case of a sparking or arcing condition, an outputwill appear on conductor and will be fed to the amplifier circuit 92. I

The amplifier circuit 92 includes an operational amplifier 278 whichincludes a variable feedback resistor 280 to vary the gain of theamplifier 278. The output of the amplifier 278 is fed to the rectifiercircuit which is of substantially identical configuration to thatdescribed in conjunction with the rectifier circuits 56 and 60.

Particularly, the rectifier circuit 96 includes an operational amplifier284 which includes an input resistor 286, a feedback resistor 288, therectifying diode 290, a feed forward resistor 296, a summing node 294and an input resistor 296 for the summing node 294. Thus, the outputsignal at node 294 is the absolute value of the input signal being fedfrom the operational amplifier 278 and the signal at node 294 isinverted by means of an inverting and buffer operational amplifier 298.The output signal from the operational amplifier 298 is fed to theoutput trigger circuit, and particularly to the inverting input of anoperational amplifier 300. The operational amplifier 300 alsoincludes a.secondi input from a. sensitivity setting circuit 302 which includes a;potentiometer 304 connected between a. positive 115- volt potential andground and a current limiting resistor 306. Thus; an output triggerpulse is' generated at an output terminal: 310: whenever the outputsignal from the operational amplifier 298 exceeds the setting onpotentiometer 304.

Referring back to FIG. 4'; there is illustrated a preferred form ofcrowbarscircuit to which the output trigger pulse at terminal 310 isfed. Particularly, the signal on input. terminal 310 is fed through aresistorr3l4 -to an isolation pulse transformer 316, the transformer 316including a primary winding 318 and a secondary 'winding 320magnetically coupled thereto. The output of the pulse transformer 316 isfed to the gate circuit of a control controlled rectifier 322 through adiode 324. The controlled rectifier 322 is connected to a. source ofdirect current potential through a: resistor 326 and a reset'button; 328has been provided to stop conduction of the controlled rectifier 322manually'by the operator, upon clearing: of the condition. which: causedthe sparking or arcing. The conduction of controlled rectifier 322generates an output pulse signal through pulse transformer 330, thesecondary of which is connected between the gate cathode circuit of acrowbar controlled rectifier 334. The crowbar controlled rectifier 334'is connected between the positive buss, at a terminalz336 and thenegative. buss, atterminal' 338;

The: output circuit also includes. a. capacitor 340 which,

i when the control rectifier 322 isnonconductiye, is chargedfrompositive to negative through a circuit including the resistor 326, adiode 342', the: capacitor 340 and a diode 344 connected to groundmwhemthe controlled rectifier 322' conducts,,the capacitor 340r dischargesthrough a circuitincluding the primary windingiof the pulse transformer330; a resistor 346,.a diode 348, the capacitor 340 and the controlledrectifr er322ito: generate a steep wave front pulse for use by theoutput pulse transformer 330:

While it will be apparent. that: the preferred embodiments of the.invention disclosedarewellfcalculated to fulfill the objectsabove state,it. will be appreciated that the. invention is susceptible tomodification, variation and change without de'- parting from: theproper'scope-orfair meaning of thesubjoined 7 claims.

I..ln a circuittfor sensing; the'sudden deviation of thecurrentrelative: to. the voltage in a load: circuit and generating an outothercurrent and: voltage. characteristic for generating the outputsignal'when saidcharacteristics becomeunequaldue to thesuddennessofithe-deviatiomexceeding the response. time.

2. The improvement. of: claim: 1. wherein said multipliercircuitmeansvariest-the-characteristic of the sensed current to adjustzthemagnitudexofsaidcurrent to equal themagnitude'of saidrvoltage.

3. The improvement-oi claim-2 wherein saidmultiplier circuit meansincludesa-quadrant multiplier'circuit having firstand-second;inputcircuits, saidfirst input circuit being fed a currentsignalfromsaid sensingmeans.

4'. The improvement ofclaim=3further includingfeedback.

circuit meansfor sensing thei'characteristic of said voltageandprovidinga'an inputsignal; in responsethereto the secondinput:

of said quadrantmultiplier circuit:

5; The improvement; of claim-Awhereinsaid feedback circuitzmeansalsoincludes. means for sensing the characteristic of said current and a.circuit for correlating said voltage and current characteristics. p

6. The improvement of claim 5 wherein said feedback circuit includes asummingnod'e for summing said current and voltage characteristics. w

-7. The improvement of claim 6- wherein said feedback circuit meansincludes a rectifier connected to said voltage sensing circuit, a secondrectifier for sensing. .the varied characteristics of said current andan inverter. circuit connected to one of said rectifiers, the outputofs'aidrectifiers being fed to said summing node.

8. The improvement of claim 7 wherein said summing node providesanoutput signal which is substantially zero when said rectified and.inverted signal is equal to said rectified signal.

9. The improvement of" claim 8 wherein the output ofsaid summing. nodeis fed to-second input of 'said quadrant multiplier circuit, the outputof said quadrant output circuit being a function of the product of said.current signal and said summing node signal.

10. The improvement of claim 9 wherein said quadrant multiplier circuitgenerates an output signal in response to said current signal andsumming summing node signal to multiply the current signal to a levelequal to the magnitude of said voltage signal.

11. The improvement of claim- 10 wherein said output circuit meansincludes a su'btracter circuit, the input of said subtracter being.responsive to said multiplied current signal and said voltage signal,the output of said subtracter being substantially zero whensaidmultiplied. current and voltage characteristics are equal.

12'. The improvement of claim 7 wherein said rectifier in"- cludesanroperational amplifier having a feedback loop, said operationalamplifier being responsive to an alternating current inputsignal, saidoperational amplifier further including a summing node anda feed-forwardcircuit, said feedback and feed-forward circuits generating. afull wave,rectified output signal in responseto-said input alternating currentsignal; andsaid' feedback loop including a high gain driver, said drivergenerating a high gain output signal for said second input to saidquadrant multiplier circuit, said: driver output being a functionoftheresistance of said load circuit.

13. The improvement of'claim 7 wherein said'feedba'ck loop generates asignalfor said second input in response to said voltage and currentcharacteristics in accordance with a function defined by said voltagedivided by said current;

14. The improvement of claim 1 wherein said multiplier circuit meansincludesa first and second input; said first input being a. function ofsaidsensed' current signal and said second input being-afunctionofsaidvoltage divided by said current.

15; The: improvement of claim 1 wherein said load circuit includes anvelectrochemicalpainting apparatusforapplyin'g a' layer of paint toasurface wherein the thicknessof paint in the load; circuit: determinesthe' resistance of said load circuit, the

variation of said. characteristic being a function of the re sistanceof'saidIOad-circuit.

16'. The: improvement of'claim l5 wherein said' multiplier circuit meansvariesthe-characteristicof the sensed currentte providing an inputsignal in response thereto to the secondinputrofsaidquadi'antimultiplier circuit.

18'. Theimprovementiof: claim 17 wherein said feedback voltage andcurrent characteristics and generating an output signal'when saidcharacteristics deviate, one from the other;

19'. The improvementof claim 18 wherein'the output'of said summingnodeis fedto the input circuit of said qua'drant multiplier. circuit, theoutput of said'quadrant circuit being a funccircuit" means includes asumming node for correlating said tion of the product of the inputcurrent signal and the output signal from said summing node, the summingnode signal being a function of the resistance of the load.

20. in a circuit for sensing the sudden deviation of a current relativeto the voltage in a load circuit wherein the sensing circuit has aninherent response time, the method of generating an output signal inresponse to the sudden deviation comprising the steps of sensingcharacteristic of load current and the load voltage, varying thecharacteristic of one of the sensed current and voltage in response tothe other of the sensed current and voltage for equalizing the sensedcharacteristic of both the current and voltage and generating the outputsignal when said characteristics become unequal in response to the timeof the sudden deviation exceeding the response time.

21. The method of claim wherein said characteristic varying stepincludes generating an output signal which is a function of said currentsignal and a multiplication factor signal to adjust the current signalso that the current signal is equal in magnitude to the voltage signal.

22. The method of claim 21 wherein said multiplication signal is afunction of both said voltage and said current signals in accordancewith a function defined by the voltage signal divided by the currentsignal.

23. The method of claim 22 wherein said multiplication signal is ameasure of the resistance of the load'eircuit.

24. The method of claim 23 further including the step of sensing thecurrent signal with reactive impedance correction circuit, and adjustingthe current signal in accordance with a function of the rate of changeof current with respect to time in the load circuit.

25. The method of claim 24 wherein said multiplier signal is utilized tocontrol the resistance of the load.

1. In a circuit for sensing the sudden deviation of the current relativeto the voltage in a load circuit and generating an output signal inresponse thereto, the improvement comprising sensing means for sensing acharacteristic of the load current and the load voltage, multipliercircuit means connected to one of said current and voltage sensing meansfor providing one input to said multiplier circuit means, saidmultiplier circuit including means for varying the characteristic ofsaid one of the sensed current and voltage in response to The other ofthe sensed current and voltage for equalizing the sensed characteristicof both the current and voltage, said multiplier circuit having aninherent response time and output circuit means connected to beresponsive to said equalized and the other current and voltagecharacteristic for generating the output signal when saidcharacteristics become unequal due to the suddenness of the deviationexceeding the response time.
 2. The improvement of claim 1 wherein saidmultiplier circuit means varies the characteristic of the sensed currentto adjust the magnitude of said current to equal the magnitude of saidvoltage.
 3. The improvement of claim 2 wherein said multiplier circuitmeans includes a quadrant multiplier circuit having first and secondinput circuits, said first input circuit being fed a current signal fromsaid sensing means.
 4. The improvement of claim 3 further includingfeedback circuit means for sensing the characteristic of said voltageand providing an input signal in response thereto the second input ofsaid quadrant multiplier circuit.
 5. The improvement of claim 4 whereinsaid feedback circuit means also includes means for sensing thecharacteristic of said current and a circuit for correlating saidvoltage and current characteristics.
 6. The improvement of claim 5wherein said feedback circuit includes a summing node for summing saidcurrent and voltage characteristics.
 7. The improvement of claim 6wherein said feedback circuit means includes a rectifier connected tosaid voltage sensing circuit, a second rectifier for sensing the variedcharacteristics of said current and an inverter circuit connected to oneof said rectifiers, the output of said rectifiers being fed to saidsumming node.
 8. The improvement of claim 7 wherein said summing nodeprovides an output signal which is substantially zero when saidrectified and inverted signal is equal to said rectified signal.
 9. Theimprovement of claim 8 wherein the output of said summing node is fed tosecond input of said quadrant multiplier circuit, the output of saidquadrant output circuit being a function of the product of said currentsignal and said summing node signal.
 10. The improvement of claim 9wherein said quadrant multiplier circuit generates an output signal inresponse to said current signal and summing summing node signal tomultiply the current signal to a level equal to the magnitude of saidvoltage signal.
 11. The improvement of claim 10 wherein said outputcircuit means includes a subtracter circuit, the input of saidsubtracter being responsive to said multiplied current signal and saidvoltage signal, the output of said subtracter being substantially zerowhen said multiplied current and voltage characteristics are equal. 12.The improvement of claim 7 wherein said rectifier includes anoperational amplifier having a feedback loop, said operational amplifierbeing responsive to an alternating current input signal, saidoperational amplifier further including a summing node and afeed-forward circuit, said feedback and feed-forward circuits generatinga full wave, rectified output signal in response to said inputalternating current signal; and said feedback loop including a high gaindriver, said driver generating a high gain output signal for said secondinput to said quadrant multiplier circuit, said driver output being afunction of the resistance of said load circuit.
 13. The improvement ofclaim 7 wherein said feedback loop generates a signal for said secondinput in response to said voltage and current characteristics inaccordance with a function defined by said voltage divided by saidcurrent.
 14. The improvement of claim 1 wherein said multiplier circuitmeans includes a first and second input, said first input being afunction of said sensed current signal and said second input being afunction of said voltage divided by said current.
 15. The improvement ofclaim 1 wherein said load circuit includes an electrochemical paintingapparatus for applying a layer of paint to a surface wherein thethickness of paint in the load circuit determines the resistance of saidload circuit, the variation of said characteristic being a function ofthe resistance of said load circuit.
 16. The improvement of claim 15wherein said multiplier circuit means varies the characteristic of thesensed current to adjust the magnitude of said current to equal themagnitude of said voltage.
 17. The improvement of claim 16 wherein sadmultiplier circuit means includes a quadrant multiplier circuit havingfirst and second input circuits, said first input circuit being fed acurrent signal from said sensing means, and feedback means for sensingcharacteristic of said voltage and said current, and providing an inputsignal in response thereto to the second input of said quadrantmultiplier circuit.
 18. The improvement of claim 17 wherein saidfeedback circuit means includes a summing node for correlating saidvoltage and current characteristics and generating an output signal whensaid characteristics deviate, one from the other.
 19. The improvement ofclaim 18 wherein the output of said summing node is fed to the inputcircuit of said quadrant multiplier circuit, the output of said quadrantcircuit being a function of the product of the input current signal andthe output signal from said summing node, the summing node signal beinga function of the resistance of the load.
 20. In a circuit for sensingthe sudden deviation of a current relative to the voltage in a loadcircuit wherein the sensing circuit has an inherent response time, themethod of generating an output signal in response to the suddendeviation comprising the steps of sensing characteristic of load currentand the load voltage, varying the characteristic of one of the sensedcurrent and voltage in response to the other of the sensed current andvoltage for equalizing the sensed characteristic of both the current andvoltage and generating the output signal when said characteristicsbecome unequal in response to the time of the sudden deviation exceedingthe response time.
 21. The method of claim 20 wherein saidcharacteristic varying step includes generating an output signal whichis a function of said current signal and a multiplication factor signalto adjust the current signal so that the current signal is equal inmagnitude to the voltage signal.
 22. The method of claim 21 wherein saidmultiplication signal is a function of both said voltage and saidcurrent signals in accordance with a function defined by the voltagesignal divided by the current signal.
 23. The method of claim 22 whereinsaid multiplication signal is a measure of the resistance of the loadcircuit.
 24. The method of claim 23 further including the step ofsensing the current signal with reactive impedance correction circuit,and adjusting the current signal in accordance with a function of therate of change of current with respect to time in the load circuit. 25.The method of claim 24 wherein said multiplier signal is utilized tocontrol the resistance of the load.